1. Field of the Invention
The present invention relates to an oil (or hydraulic) pressure controller (including device), for one with an automatic transmission, for the purpose of reducing shock during a gear shift. More particularly, the present invention relates to the hydraulic pressure controller (including device) and the use thereof to control line pressure during the shift mode of the automatic transmission according to the vehicle speed and throttle opening degree.
2. Background
Tokko No. Sho 61-48021 and Tokko No. Hei 7-92140 disclose hydraulic pressure control devices for an automatic transmission. Tokko No. Sho 61-48021 discloses a hydraulic pressure controller (including device) for an automatic transmission comprising: a friction element operative to a line pressure that chooses a power train path of a transmission mechanism connected to an engine output shaft; a line pressure control valve controlling the line pressure applied to the friction element; a shift solenoid applying the line pressure to or removing the same from the friction element; a control means for controlling a line pressure adjusting valve and a shift solenoid by comparing a current gear and a predetermined gear located in a shift map with signals from an engine load sensor and a vehicle speed sensor.
The oil (or hydraulic) pressure controller controls the line pressure at a different pressure during a shift mode of changing friction elements from as opposed to a non-shift mode and regulates the line pressure at a lower pressure to match up to an engine load read or measured by an engine load sensor, which attenuates or reduces a shift shock.
Tokko No. Hei 7-92140 discloses a hydraulic pressure controller for an automatic transmission, which controls a line pressure applied to a friction element of the automatic transmission according to information of an engine load detected or measured by an engine load detecting means, and a vehicle speed detected or measured by a vehicle speed detecting means so as to attenuate or reduce a shift shock when a selector lever is manually shifted.
Further, in an automatic transmission with a one-way clutch, the one-way clutch synchronizes with a gear shift to attenuate a shift shock during a downshift to the gear operative with the one-way clutch.
However, there is a recent tendency to reduce the number of one-way clutches to make the automatic transmission smaller. For example, there is an automatic transmission that has only one gear operative with the one-way clutch.
During downshift to a gear not operative with the one-way clutch of such automatic transmission, a clutch engagement timing is adjusted to have an engine rotational speed increased to synchronize rotational speeds of engaging members of the clutch in order to attenuate the shift shock.
A line pressure is generally changed or adjusted during a gear shift as a means for adjusting the clutch engagement timing of the downshift. Thus, if the line pressure is lowered during the gear shift, the clutch engagement timing is delayed and the engine rotational speed is increased a great amount to synchronize the engaging members where a high engine rotational speed is required. If the line pressure is raised during the gear shift, the clutch engagement timing is advanced and the engine rotational speed is increased a small amount to synchronize the engaging members in the case that the high engine rotational speed is not required.
However, in such method of changing the line pressure during the gear shift, if the line pressure is lower than the correct pressure, the engine rotational speed exceeds the synchronized rotational speed and causes racing. If the line pressure is higher than the correct pressure, a shift shock in a direction to pull a vehicle, so-called a pullback shock, is caused since the clutch engagement is started before the engine rotational speed reaches the synchronized rotational speed.
Since the engine rotational speed for synchronization during the gear shift is corresponding to the vehicle speed, it is possible to set the line pressure according to the vehicle speed in order to control the line pressure at the correct pressure during the gear shift. For example, the clutch engagement timing is delayed during the downshift at a higher vehicle speed because it requires more synchronizing time to raise the engine rotational speed a great amount. The clutch engagement timing is advanced during the downshift at a lower vehicle speed because it requires less synchronizing time to raise the engine rotational speed a small amount.
However, in the above method of changing the line pressure during the gear shift, the correct engagement timing is not necessarily established by setting single line pressure at a vehicle speed and the shift shock is caused by the correct line pressure at the same vehicle speed in the event of "kick-down" (shift-down made by the automatic transmission in response to a driver's intentional depression of the accelerator pedal) as opposed to the situation where the accelerator pedal is released from the driver's foot differs from that in the event of kick-down from the situation that the accelerator pedal is depressed to a certain degree.
When the accelerator pedal is released, as opposed to when the accelerator pedal is depressed, it takes longer for the engine torque to increase to a certain level and for the engine rotational speed to reach the synchronized rotational speed, which causes a time lag. The shift shock is particularly evident with an automatic transmission connected to a turbo-charged engine.
In order to avoid the shock, it is possible to set a delay time after the gear shift is determined and before the gear shift signal is transmitted to a shift solenoid, in the event of kick-down when the accelerator pedal is released, so that the actual gear shift is started after the delay time since the gear shift determination and the gears are shifted after the engine torque is increased to a certain level. The delay time enables the correct line pressure for kick-down when the accelerator pedal is released and is almost the same as that for kick-down when the accelerator pedal is depressed to a certain degree.
However, in this method of setting the delay time, because the driver wants immediate acceleration by the kick-down, it is against the driver's intention to set the delay time such that an immediate response is not realized.
If the delay time is too short, the gear shift is started when the engine torque is not large enough, such that the single line pressure cannot handle the synchronization, and causes the shift shock.